First the Basics, Then the Complicated Stuff

Have you ever had occasion to wonder about someone's lack of knowledge?

As you probably saw, our own inscrutable Max Maxfield recently posted a blog on iPod/iPad/iPhone headphone output. He started by explaining some fairly fundamental analog concepts.

I emailed Max asking why he'd started off at such a simple level. He replied that, over time, he's come to realize it's not a good idea to assume everyone understands everything, including the simple stuff. A lot of EE Times community members are students. A lot of members focus on the digital domain, as opposed to analog, and many professional engineers have forgotten a lot of the fundamental concepts they no longer use on a day-to-day basis.

Almost as soon as I'd read Max's response (some might say coincidentally), I received a request for help from a friend who wanted to connect a LED to a 12VAC power source. This friend is a particularly bright guy with an MSEE, but he left engineering and went to "the Dark Side" (project management) about 30 years ago.

It's amazing what we forget. My friend sort of acknowledged this by starting with a bit of humor. "I was hoping that, if I connected the LED to the AC just with the resistor, it would work, but maybe not be as bright," he said. "But I guess, being AC, the reverse voltage causes the current to flow the other way -- who knows with modern LEDs these days, anything can happen -- causing the LED to glow bright black in the negative cycle, and the eye would cancel all of the bright white and the bright black, and we'd see nothing."

I explained how to calculate the current when using a LED. I also explained that he would have to protect the LED with a diode in reverse polarity across the LED. He came up with the following circuit based on my description.

Observe the "+" and "-" annotations marked on the AC. Also observe that no current will ever flow. We all can see that, right?

Then I started to think of other instances when I've been surprised by people's lack of knowledge. Six or seven years ago, we hired an EE graduate straight out of university. A few months later, I was reading a Jack Ganssle blog post, from which I've extracted the following quote:

Long ago I worked with an engineer who had applied for a job at Cape Canaveral. The tour seemed to always come back to a panel of beautiful controls just crying out for some tactile interaction. A big bundle of wires coming trailing on the floor was cut, proving the box wasn't connected to anything, and my friend finally succumbed and twisted a knob. Klaxons suddenly blared all over the blockhouse! The panel was a test; management didn't want to hire someone who pressed buttons in a launch complex. He didn't get the job.

I found this very amusing, so I told the story to the guys in the lab. They all laughed, except the young guy who asked, "What's Cape Canaveral?" (He didn't know what Cape Kennedy was, either.)

The bottom line is that there is a lot of stuff we don't know, some stuff we forget, and some stuff we must pass on to other generations. So all I can say is "Keep up the good work, Max."

How about you? Have there been any occasions when you discovered that you'd forgotten some fundamental concept? How about someone being ignorant of something you would absolutely have assumed that person knew?

It's funny to see someone make simple assumptions that are probably wrong.

With the simple circuit and two "diodes" in series opposition one might conclude that only leakage current would flow for either polarity of input. But simple dismissal of the circuit may not be quite right.

Most LED's have extremely low reverse voltage capability. Most around 5-6V, or if they are more advanced, they have a parallel bulk protection diode in place and have a reverse voltage rating of only .8-1.2V.

In either case and with this circuit it's highly likely that current will flow for the AC half cycle shown.

In the case of Vr breakdown it might be 6V or so....add the protection diode Vf and you'd see something of the order of 7V across the diodes and about 9V across the resistor (about 17v peak from the AC 12v input). Current will flow (9/R) and it's unlikley to damage the LED (and of course you won't get any black light out of it....now that was a giggle)

There is no doubt that the circuit is non-ideal, but explaining that you must consider both polarities of input and the characteristics of the LED might have been better than dismissal.

@AndrewAPTemple: And, I look forward to more interaction with the community (as opposed to only reading the articles), and the jokes!

I lot of us have formed lasting friendships via EETimes and its sister sites -- some of us even manage to meet up at conferences. Maybe you will be able to attend some of these conferences after you've finished being a student. Where abouts are you based?

You cannot help but forget things -- especially things you don't use on a daily basis -- one of the best ways to stay on top of things (I think) is to have hobby projects that are outside of your usual work activities, because when you have a task to do you have to learn how to do it, and as long as you are learning stuff you seem to be better able to remember other stuff.

I'll keep those words in mind, especially when I finally I got into this professional, managerial world I keep hearing about.

And, I look forward to more interaction with the community (as opposed to only reading the articles), and the jokes!

@antedeluvian: I find it quite disheartening when I put several hours into a blog and it seems to fall on deaf ears.

I knwo just what you mean -- sometimes I slog away at a column ... and no one says anything ... I'd like to think it was because they were left speechless by my brilliance, but I fear thsi is not the case LOL

On the other hand, when I post a blog like my recent Thanks, Dad! that gets a bunch of comments, then I bounce aroudn with a great big sloppy grin on my face :-)

@AndrewAPTemple: I first off want to say hello to the community of EE Times! Even after being a member of the site for a while now, this is first time I have ever decided to leave a comment!

Hello there -- welcome aboard :-) Hopefully we'll be seeing a lot more of you (comment-wise).

I make a lot of jokes about management and managers, but they do provide a necessary function (being the butt of my jokes, for example :-)

You cannot help but forget things -- especially things you don't use on a daily basis -- one of the best ways to stay on top of things (I think) is to have hobby projects that are outside of your usual work activities, because when you have a task to do you have to learn how to do it, and as long as you are learning stuff you seem to be better able to remember other stuff.